December 9, 2013

CENTER FOR VETERINARY BIOLOGICS NOTICE NO. 13-18

TO: Biologics Licensees, Permittees, and Applicants

Directors, Center for Veterinary Biologics

Veterinary Services Leadership Team

FROM: Byron E. Rippke /s/ Byron E. Rippke

Acting Director

Center for Veterinary Biologics

SUBJECT: Discontinuing the Use of RelPot Software

I. PURPOSE

This Notice pertains to all licensees using relative potency immunoassays for serial 

release testing of veterinary biologics. It states that RelPot software will no longer 

be used by the Center for Veterinary Biologics (CVB) and provides guidance for 

firms to transition to commercial software for estimating relative potency (RP) in 

approved assays.

II. BACKGROUND

RelPot software for estimating RP in immunoassays has been distributed by the 

CVB as a convenience to licensees since at least 1991. The most recent version was 

developed under the Windows 95 operating system. It used an automated segment 

selection method described in Supplemental Assay Method (SAM) 318. SAM 318, 

Section 1.4, notes that the method “is based on an algorithm that has no internal 

validity” and requires external validation. CVB is discontinuing the use of RelPot 

software and the method of SAM 318 by its laboratories. Firms with approved 

potency assays that have utilized RelPot are advised to transition to the use of 

commercial software for serial release.

III. SCOPE

This guidance refers to relative potency immunoassays approved for serial release of 

veterinary biologics. This guidance addresses the estimation of relative potency in 

such assays; it does not affect activities which do not require RP estimation, such as 

reference monitoring.

IV. ACTION

 A. The CVB will discontinue the use of RelPot software after December 31, 

 2013. Licensed firms may continue to use RelPot software for serial release 

Animal and Plant

Health Inspection

Service

Veterinary Services

Center for Veterinary 

Biologics

1920 Dayton Avenue

PO Box 844

Ames, IA 50010

(515) 337-6100
CENTER FOR VETERINARY BIOLOGICS NOTICE NO. 13-18

Page 2

 per approved Outlines of Production and Special Outlines through the end of 

 calendar year 2015. The disposition of all serials will follow the approved Outline of 

 Production. 

B. Before January 1, 2016, firms should develop proposals for transitioning each 

approved assay currently using RelPot software for serial release to other software, 

and submit such proposals to CVB Policy, Evaluation, and Licensing (PEL) for 

consultation and approval. Firms may propose an alternate time line for transitioning 

assays already approved or close to approval as of Jan. 1, 2014.

C. Transition proposals should demonstrate that the proposed procedure and software 

package will produce appropriate RP estimates suitable for serial release. Provide data 

to support the proposal. Identify the software in the Outline of Production or Special 

Outline. Specify the software settings either in the outline or in a separate document 

such as a standard operating procedure, to be included with the transition proposal. 

Specify the region of the response curves that will be utilized for RP estimation. For 

example, full curves may be fit by parallel nonlinear (e.g. logistic) functions, or 

pseudo-linear regions may be fit with parallel linear regressions. Automated segment 

selection methods should not be used. 

D. Features to consider in software for serial release are the ability to fit a suitable model 

with the appropriate parameter constraints, estimate RP, provide a graphical depiction 

of the raw data and model fit, and evaluate validity criteria such as parallelism. While 

the CVB does not endorse specific software packages, the CVB Statistics Section may 

be able to provide some technical advice on implementation within some of the 

available commercial software it is familiar with.

E. In most cases, evaluation of the new software (and the method for using it) for a 

particular assay may be achieved by demonstrating the suitability of its performance 

on a representative historical data set. A set of at least 10 serial tests should typically 

be sufficient. In some cases, fewer tests may be justified, while highly variable assays 

or nonstandard analysis methods may require more data. Suitability means that the 

model (e.g. linear regression), data subset (e.g. limited to the pseudo-linear region if 

applicable), and validity criteria are appropriate for relative potency estimation in light 

of the procedure being replaced. 

F. For confirmation of dating studies initiated prior to the transition, data from before and 

after the transition may be analyzed using the post-transition software and method.

V. IMPLEMENTATION/APPLICABILITY

This policy will be effective immediately from the date of this Notice. The applicability of 

this policy is defined in Section III (Scope).

 

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